Chapter 2 students - 104.5 o 0.96 bent geometry O-H bond is...

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Unformatted text preview: 104.5 o 0.96 bent geometry O-H bond is highly polarized (H: partially positively charged, O partially negatively charged) The Water Molecule 1 MCDB310 Chapter 2: Water electrostatic attraction between O and H of neighboring water molecules highly directional intermolecular association: Hydrogen bond The Hydrogen Bond longer and much weaker than covalent bond (20 kJ/mol vs. e.g. C-C, 348 kJ/mol) 2 MCDB310 Chapter 2: Water + - not restricted to water; can also form between other electronegative proton donors and acceptors (e.g. C=OH-N) 3 MCDB310 Chapter 2: Water Biologically Important Hydrogen Bonds Quiz: What are the Hydrogen Acceptors and Donors in Aspartame? 4 MCDB310 Chapter 2: Water 5 MCDB310 Chapter 2: Water Geometry of Hydrogen Bonds Hydrogen bonds are strongest when all three participants are arranged in a straight line Hydrogen Bonds in Ice each water molecule is tetrahedrally arranged and makes H-bonds with four other water molecules upon melting, ~15% of H-bonds are broken open ice structure causes water to expand upon freezing 6 MCDB310 Chapter 2: Water Water as a Solvent 7 MCDB310 Chapter 2: Water Hydrophilic (water loving) substances polar, charged substances (e.g. salts such as NaCl) polar, uncharged substances (e.g. sugars such as glucose) Hydrophobic (water fearing) non-polar substances (e.g. gases, oil) Very good for: Poor for: Charged Substances 8 MCDB310 Chapter 2: Water held together by electrostatic interactions strength of electrostatic interaction depends on- number of charges- distance between charges- dielectric constant of solvent r (measure of its ability to mask/shield charges) NaCl Na + + Cl- Electrostatic Interactions 9 MCDB310 Chapter 2: Water Coulombs law: F: force between two electrical charges q 1 and q 2 : proportionality constant r: distance between charges r : dielectric constant of solvent (water: 78.5 , benzene: 4.6) water weakens electrostatic interactions 2 2 1 r q q F r Most Salts Readily Dissolve in Water 10 MCDB310 Chapter 2: Water Explanation: Entropy of salt increases upon dissolution Dissolution of Polar, Uncharged Substances 11 MCDB310 Chapter 2: Water Glucose water soluble because solute/solute H-bonds are replaced by water/solute H-bonds that are energetically more favorable (entropy!) Hydrophobic Compounds 12 MCDB310 Chapter 2: Water non-polar gases (e.g. O 2 , CO 2 ) organic compounds with long aliphatic chains (fatty acids), phenyl groups etc. (oils, lipids, wax) Soluble only in non-polar solvents (e.g. benzene, hexane) Hydrophobic Compounds 13 MCDB310 Chapter 2: Water Non-polar gases: Electrons are shared equally by both atoms (N 2 , O 2 ) or bond dipols cancel each other out (CO 2 ) 14 MCDB310 Chapter 2: Water Hydrophobic Compounds in Water...
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This note was uploaded on 04/05/2009 for the course MCDB 310 taught by Professor Walter during the Spring '09 term at University of Michigan.

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Chapter 2 students - 104.5 o 0.96 bent geometry O-H bond is...

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